1. Field of the Invention
The present invention relates to a manually operated small pump for the delivery under pressure of micronized liquid and/or thick substances. Known
2. Description of the Background
Known are many types of pumps manually operated applicable on containers of liquid substances, for the delivery of liquid substances in micronized or nebulized form.
The simplest types of these pumps have the disadvantage that both nebulization of the liquid delivered and the pressure under which it is ejected out of the nozzle of the cap applied on each pump depend on the rate of actuation of the pump itself and on the pressure exercised thereon.
U.S. Pat. No. 4,228,931 and French Pat. No. 2,097,353, respectively, disclose two manual small pumps capable of delivering the liquid only when it reaches a minimum predetermined pressure inside of a pressure chamber which each pump is provided with.
This small pump comprises a seal moved by the action of a spring, said seal covers a hole for the passage of the liquid to the delivery can and it rises from this hole only after having imparted a predetermined pressure to the liquid contained in a pressure chamber making part of the same pump.
Under rest conditions, the above spring pushes the seal on a base integral with a movable stem making part of the pump: after the liquid present in the pressure chamber has reached the pressure sufficient to overcome the action of the spring on the seal, the seal rises from its sealing base making free the hole for the passage of the liquid towards the delivery cap.
Pumps of this type operate in a satisfactory manner, but they have a disadvantage consisting of the presence of the spring working on the seal as above-mentioned. In fact, the use of such springs increases the production cost of the pumps owing to both the cost of the springs and the cost of assembling them into the pumps (it should be noticed that the parts of these pumps have very small sizes, so that the right assembling of several different parts inside of the pumps is dificult): furthermore, being the spring made of metal or metal alloys, their presence can be incompatible with the use of corrosive liquids or the like.